Mist suppression in electroplating solutions

ABSTRACT

In accordance with certain of its aspects, this invention relates to novel compositions and to a process for suppressing mist formation in an aqueous composition which comprises incorporating hydrophobic particles having a particle size of 0.002-100 microns into said aqueous compositions. The process is applicable, for example, to chromium electroplating solutions.

United States Patent 52 US. Cl. ..204/51, 204/910. 1 [51] Int. Cl...C23b 5/06 [58] Field ofSearch ..204/41,51, 1.01

[56] References Cited UNITED STATES PATENTS 3,150,015 9/1964 Boyer et al..148/6.2 2,992,171 7/1961 MacLean et al.

2,999,798 9/1961 Eitel et a1 ..204/41 X 3,108,933 10/1963 Johnson..204/51 Chessin [45] Apr. 18, 1972 [54] MIST SUPPRESSION IN 3,152,97110/1964 Tomaszewski et a] .204/41 ELECTROPLATING SOLUTIONS 3,268,3078/1966 Tomaszewski et al. ....204/4l X 3,356,467 1 19 7 B t l [72]Inventor: Hyman Chessin, Birmingham, Mich. 2/ 6 6 a 204/41 X [73]Assignee: M & T Chemicals Inc., New York, NY. FOREIGN PATENTS ORAPPLICATIONS 29 337 10/1930 Australia ..204/1 l 1 I22] F'led Sept 25 968161,199 2/1963 U.S.S.R. .204/1 [21] Appl. No.: 762,624

Primary Examiner-G. L. Kaplan Att0rney-Lewis C. Brown and Kenneth G.Wheeless [57] ABSTRACT In accordance with certain of its aspects, thisinvention relates to novel compositions and to a process for suppressingmist formation in an aqueous composition which comprises incorporatinghydrophobic particles having a particle size of 0.002- 100 microns intosaid aqueous compositions. The process is applicable, for example, tochromium electroplating solutions.

8 Claims, No Drawings MIST SUPPRESSION IN ELECTROPLATING SOLUTIONS Thisinvention relates to novel suppressant compositions and to the use ofsuch compositions in plating processes. More particularly, thisinvention relates to compositions which may be used in electrolyticmetal plating operations to reduce losses of the plating bath due tofume and/or spray production.

As is well known to those skilled in the art, electroplating baths (suchas chromium plating baths) may be characterized by high fume or spraylosses. The production of fumes from an electroplating bath may beobjectionable from a health viewpoint because of pollution and wasteproblems. The use of various additives in electroplating bathcompositions has not been entirely satisfactory since such additives areusually surfactants. Such surfactants may be expensive and may produceadverse effects upon the electroplated article which is ultimatelyproduced.

Other attempts to reduce fume and spray production have involved the useof floating plastic materials such as ping pong balls in order to reducethe effective surface area which may produce such fumes and sprays. Suchattempts, however, have not been entirely satisfactory because it hasbeen found that such floating articles may pick up particles of wax orother foreign materials and deposit such matter upon the surface of thearticle to be plated either before or after electroplating to producedefects such as streaks, pits, etc.

It is an object of this invention to provide novel compositions usefulin electroplating processes. A further object of the invention is toprovide novel fume-suppressing compositions which may be used inelectroplating processes. Another object of the invention is to provideeffective means for controlling losses in electroplating processes dueto fume and/or spray production without producing adverse effects uponthe plated articles produced.

In accordance with certain of its aspects, this invention relates tonovel compositions and to a process for suppressing mist formation in anaqueous composition which comprises incorporating hydrophobic particleshaving a particle size of 0.002-100 microns into said aqueouscomposition.

According to one of its aspects, this invention relates to a process forsuppressing the production of fumes and mists from an aqueouselectroplating bath solution which comprises passing current from ananode to a metal cathode through an aqueous electroplating bath solutioncontaining a metal compound providing metal ions for electroplatingmetal and including a blended dispersion of hydrophobic particles havinga particle size of 0.002-100 microns, to produce a plated article, andremoving said plated article from said aqueous electroplating bathsolution.

According to another of its aspects, this invention may be employed tocontrol vapor, mist, spray, or bubble formation in other liquids (suchas stripping liquors, pickling liquors, anodizing baths, etc.

The hydrophobic particles which may be used according to the presentinvention may be composed of inert water repellent material which doesnot appreciably dissolve in the particular electroplating bath solutionin which the production of fumes is to be inhibited or reduced. As usedherein, the term inert" is meant to refer to materials which donot reactwith the aqueous electroplating bath solutions. Typical hydrophobicpolymeric materials which may be used according to the invention includepolyfluorinated hydrocarbons, polypropylene, polyvinyl chloride, andpolystyrene. Other natural or artificial hydrophobic materials which maybe used include talc, wax, alumina, polymers or copolymers of styrene,butadiene, acrylonitrile, vinyl acetate, vinyl chloride, etc.;diatomaceous earth; silicates, e.g. sodium silicate; insolublecarbonates; insoluble carbides; etc., or mixtures of such materials.Silica which has been coated with a polysiloxane (such as polyalkylpolysiloxanes, e.g. characterized by dimethylsiloxy groups ordiethylsiloxy groups) is especially useful. Finely divided silica whichcontains a surface coating of hydrolyzed dimethyl-dichlorosilane is apreferred hydrophobic material for use according to the invention.Typically, the particles employed according to the process of theinvention may be finely divided, naturally occurring or artificiallyprepared materials. They may be spherical, angular, chunky, ovular,elongated or platelet-shaped. Preferably, the particles may have anaverage diameter of 0.002- microns, typically 0.005-10 microns, andpreferably 0.0l-l.0 microns.

The density of such particles should be such as to allow the particlesto remain dispersed in the aqueous electroplating bath composition and,preferably, to float upon the surface of said aqueous electroplatingbath composition or remain in dispersion at the gas-liquid interface ofsaid aqueous electroplating bath composition. Thus, coated hydrophobicparticles may be employed which have a density which would ordinarilynot permit said particles to remain in dispersion, providing that thecoating (which may be obtained by chemical or physical means) permitsthe particles to remain in the vicinity of the gas-liquid interfaceduring the electroplating operation.

Suitable hydrophobic materials which may be used in accordance with theinvention are characterized as materials which when thoroughly blendedin a 5 percent (volumevolume) aqueous sulfuric acid solution, followedby bubbling air or other non-reactive gas into said dispersion for aperiod of 30 minutes and permitting the resulting mixture to settle for30 minutes, produces a two-phase system wherein the upper phase containshydrophobic particles at the gas-liquid interface, and the lower phaseis substantially free of said particles. The particles which separate atthe gas-liquid interface may be noted to have formed a complex structurein which the gas or air has been entrained in a cellular or foam-likestructure with essentially none of the aerated particles appearing inthe lower liquid phase of the dispersion after said 30 minute settlingtime. In particular, the hydrophobic materials which are used accordingto the invention are such that when 1 gram of said hydrophobic materialis blended with 400 ml of an aqueous solution of 5 percent(volume-volume) sulfuric acid in a typi cal laboratory blender (such asa Waring brand blender) at low speed for 3 minutes a dispersion isformed which may be broken by bubbling a gas (typically air) throughsaid dispersion using a 1-ml straight pipette as a gas wand for 30minutes, followed by a settling time of 30 minutes to produce a twophasesystem. After settling, the hydrophobic materials useful in thepresentinvention form an upper phase which covers the surface of the lowerliquid phase containing the 5 percent aqueous sulfuric acid. The upperphase contains hydrophobic particles in complex, porous structureswherein the hydrophobic particles are entrained with the gas formingirregular bubbles or cells of liquid, said irregular bubbles or cellssurrounding the hydrophobic particles. The hydrophobic particles arethus essentially removed from the aqueous sulfuric acid solution whenthe air or other gas is'thoroughly mixed with the initial dispersionformed by blending the hydrophobic particles with the aqueous sulfuricacid. Other materials which are not suitable for use according to theinvention (such as hydrophilic particles) may be found to form aninitial dispersion when blended with an aqueous sulfuric acid, but donot separate into two phases when contacted with a finally dividedstream of gas.

Typical electroplating baths which may be treated in accordance with thepresent invention may include chromium electroplating baths; tinelectroplating baths; zinc electroplating baths; etc.

Thecompositions and processes of the invention have been found to beparticularly effective in chromium plating bath processes. In chromiumplating operations it is well known that the fumes and sprays producedduring the electroplating process may be particularly corrosive and maycause significant losses of plating material in the course of theelectroplatmg process.

It has been found particularly advantageous to incorporate finelydivided particulate hydrophobic particles having an average particlesize of 0.002-100 microns in diameter into a portion of the bathcomposition using a high speed blender to obtain a preliminarydispersion of the foam-suppressing particles in concentrated form.Typically, the concentration of finely divided particulate particles insuch preliminary dispersions may be -400 g/l. The preliminary dispersionso prepared may then be incorporated into the plating bath compositionin order to provide a concentration of about 0.14 grams of hydrophobicparticles per square decimeter of aqueous electroplating bathcomposition having a gas-liquid interface through which fumes or mistsof bath composition would normally escape.

A particular advantage of the invention is that the small size andhydrophobic character of the particles may result in preferentialsorption into the gas-liquid interface of the bubbles which may beformed at the electrodes. This action of the hydrophobic particlesinterferes with the spattering of such bubbles which form at theelectrodes and tends to reduce and inhibit the formation of mists orsprays by reduction of said spattering effects. In addition, it has beenfound that a stable, thin, cell-like structure containing said particlesmay be formed upon the surface of the electroplating bath so that a finepellicle remains everywhere on the surface of the electroplating bathunless the surface is being constantly and severely agitated. Thispellicle further acts to prevent spattering and fuming. Thus, accordingto the present invention, the conditions of high surface tensioncharacteristics of a normal electroplating bath are preferred and thepresence of surfactants which may lower the surface tension is notadvantageous.

The following examples are submitted for the purpose of i1- lustrationonly and are not to be construed as limiting the scope of the inventionin any way.

EXAMPLE 1 Preparation of Concentrated Dispersion A thixotropicdispersion of hydrophobic silica was prepared by blending the followingfor 1 minute using a laboratory Waring blender:

100 ml ofwater 24.0 grams chromic acid (CrO 4.8 grams hydrophobic silica(available from Degussa Corp., designated Aerosil R-972 brandhydrophobic silica); particle diameter of 0.0 10.04 microns.

The final volume of the resulting blend was about 200 ml. A l-litersample of this dispersion is sufi'rcient for initially charging anelectroplating bath contained in a tank having a surface area exposed tothe atmosphere of about 170 square decimeters. The dispersion may beprepared by the use of any highshear blending equipment or similarapparatus.

EXAMPLE 2 Four l-liter beakers containing 1 liter each of the followingTwo electrodes were immersed in each of the four l-liter samples ofchromium plating solution and a current of 10 amperes was passed throughthe solution. Gas bubbles were observed to form in each of the fourbeakers. To each beaker was added an amount of the concentrateddispersion from Example 1 sufficient to provide a hydrophobic silicaconcentration in each of the l-liter samples of chromium electroplatingsolution of 0.1 gram per square decimeter of solution exposed to theatmosphere (i.e. 0.1 gldm The fuming and spattering was almostimmediately observed to decrease. A stable foam-like coating wasobserved to form upon the surface of each of the electrolyzed samples ofchromium electroplating solution.

EXAMPLE 3 Using the chromium electroplating baths described in Example2, various articles containing metal surfaces (such as panels, rods,window crank handles, etc.) were chromium plated both with and withoutthe addition of portions of the concentrated mist suppressing dispersionof Example 1. The quality of the chromium plate on each of thechromium-plated parts from each of the baths which contained the mistsuppressing composition was then determined and compared with thequality of the chromium plate on parts which were plated in chromiumelectroplating baths without the mist suppressing dispersion ofExample 1. The results are summarized in Table Hydrophobic silica persquare decimeter of gas-liquid interface or aqueous plating solut q ltAs can be readily observed from the results of Table 1, parts plated inchromium electroplating baths containing effective amounts of the mistsuppressing compositions of the invention were found to be of excellentquality with no adverse streaking, pitting, or other defects observed inthe final chromiumplated articles.

EXAMPLE 4 Duplicate l-liter samples of the chromium plating baths ofExample 2 were prepared using the procedure of Example 1. Sufficientconcentrated mist suppressant dispersion was added to the first l-litersample of the chromium plating bath to provide a concentration of 0.1gram of hydrophobic silica per square decimeter of gas-bath liquidinterface. The second 1- liter sample of chromium electroplatingsolution was not treated with mist suppressant. Electrodes were insertedinto each sample and the solutions were electrolyzed at 10 amperes for atime period of 8 hours at a solution temperature of 55 C. After 6 hours,the volume of the untreated chromium electroplating sample had decreasedfrom 1,000 ml to approximately 940 ml, whereas the volume of the treatedl-liter sample of chromium electroplating solution was found to bedecreased to about 980 ml. From these results it can be seen that fumeand spray losses were significantly decreased according to the processof the invention by the use of the hydrophobic mist-suppressingcomposition of the invention.

EXAMPLE 5 A 300-ml sample of a solution used for metal stripping andpickling operations was prepared by combining equal volumes ofconcentrated hydrochloric acid and water. The 300-ml solution wasdivided into two -ml portions. The first 150- ml portion received nofurther treatment whatsoever and was designated as the control. To thesecond portion was added 0.76 grams of hydrophobic silica (Aerosil R-972brand hydrophobic silica). The hydrophobic silica was blended into the150-ml acid sample and then each of the two samples was transferred to aseparate 400-m1 beaker to provide identical surface areas at theair-liquid interfaces. The concentration of the hydrophobic silica interms of grams per square decimeter of air-liquid interface was 2.0 gldmTo each sample was added 20 chromium-plated screws of identical size andshape. As the chromium dissolved in each of the samples, gas wasobserved to evolve. The gas bubbles from the untreated (control)solution were large and were easily observed to break at the surface andto form droplets and mist. The gas bubbles which formed in the solutioncontaining the hydrophobic silica were observed to be small, wereentrained, and were released gently through the blanket of foam-likematerial which was observed to coat the air-liquid interface of thesecond sample which contained the hydrophobic silica. No fumes weredetected. After standing for a time period of 66 hours, the controlsample had lost a total of 20 ml in volume due to fuming andevaporation, whereas the treated solution containing the hydrophobicsilica in accordance with the invention had lost only ml of its volume.The chromiumplated screws used in the test were observed to be equallystripped and pickled from each sample.

EXAMPLE 6 A 400-ml sample of a chromium plating bath containingapproximately 240 g/l of chromic acid, 1.0 g/l of sulfate ion, and 2.0g/l of fluosilicate ion in the presence of strontium and potassium ionswas prepared as a standard mixed-catalyst, self-regulating chromiumplating bath. To this chromium plating bath composition was added 1 gramof powdered solid polypropylene wherein the average diameter of thepolypropylene particles was approximately 35 microns. The 400-ml samplewas placed in a l-liter beaker to give a concentration ofmist-suppressing agent per area of air-liquid interface of 1 gram ofpolypropylene powder per square decimeter of air-liquid interface. Onelectrolysis of the treated composition in the l-liter beaker, sprayformation was completely eliminated and a mist-suppressing layer wasobserved to form,

at the air-liquid interface.

Although this invention has been illustrated by reference to specificembodiments, modifications thereof which are clearly within the scope ofthe invention will be apparent to those skilled in the art.

I claim:

1. A process for suppressing mist formation in a chromium electroplatingbath solution which comprises incorporating an effective amount ofhydrophobic particles having a particle size of 0.002- microns into saidaqueous composition and wherein the concentration of said particles isat least 0.04 grams per square decimeter of gas-liquid interface.

2. A process as claimed in claim 1 wherein the hydrophobic particleshave an average diameter of 0.005-10 microns.

3. A process for suppressing the production of fumes and mists from achromium electroplating bath composition which comprises passing currentfrom an anode to a metal cathode through an aqueous electroplating bathsolution containing a chromium metal compound providing chromium metalions for electroplating metal and including an effective amount of ablended dispersion of hydrophobic particles having a particle size of0.002-100 microns to produce a plated article from said electroplatingbath solution, and wherein the concentration of said particles is atleast 0.04 grams per square decimeter of gas-liquid interface.

4. A process as claimed in claim 3 wherein the electroplating bath ismaintained at a temperature of 5l 00 C. 5. A process as claimed in claim3 wherein the concentration of the hydrophobic particles in theelectroplating bath solution is about 0.04-75 grams of hydrophobicparticles per square decimeter of aqueous electroplating bathcomposition at the gas-liquid interface.

6. A process as claimed in claim 3 wherein the hydrophobic particlescontain hydrophobic silica having an average particle diameter of0005-10 microns.

7. A novel composition containing an aqueous chromium electroplatingbath composition and an effective amount of a blended dispersion ofhgdrophobic silica particles having a particle size of 0002-10 micronswherein the concentration .of the hydrophobic particles is about 0.04-75grams of hydrophobic particles per square decimeter of aqueous acidsurface at the gas-liquid interface of the aqueous acid and theatmosphere.

8. A novel composition as claimed in claim 7 wherein the hydrophobicparticles have an average diameter of 0.005-10 microns.

2. A process as claimed in claim 1 wherein the hydrophobic particles have an average diameter of 0.005-10 microns.
 3. A process for suppressing the production of fumes and mists from a chromium electroplating bath composition which comprises passing current from an anode to a metal cathode through an aqueous electroplating bath solution containing a chromium metal compound providing chromium metal ions for electroplating metal and including an effective amount of a blended dispersion of hydrophobic particles having a particle size of 0.002-100 microns to produce a plated article from said electroplating bath solution, and wherein the concentration of said particles is at least 0.04 grams per square decimeter of gas-liquid interface.
 4. A process as claimed in claim 3 wherein the electroplating bath is maintained at a temperature of 5*-100* C.
 5. A process as claimed in claim 3 wherein the concentration of the hydrophobic particles in the electroplating bath solution is about 0.04-75 grams of hydrophobic particles per square decimeter of aqueous electroplating bath composition at the gas-liquid interface.
 6. A process as claimed in claim 3 wherein the hydrophobic particles contain hydrophobic silica having an average particle diameter of 0.005-10 microns.
 7. A novel composition containing an aqueous chromium electroplating bath composition and an effective amount of a blended dispersion of hydrophobic silica particles having a particle size of 0.002-100 microns wherein the concentration of the hydrophobic particles is about 0.04-75 grams of hydrophobic particles per square decimeter of aqueous acid surface at the gas-liquid interface of the aqueous acid and the atmosphere.
 8. A novel composition as claimed in claim 7 wherein the hydrophobic particles have an average diameter of 0.005-10 microns. 